Heat-shield element for a compressor-air bypass around the combustion chamber

ABSTRACT

A heat-shield element ( 14 ), for lining a combustion-chamber wall ( 13 ), the chamber wall has a first wall ( 17 ) with a hot side ( 18 ) which can be loaded with a hot medium, a cold side ( 19 ) which lies opposite the hot side ( 18 ), and a circumferential edge ( 24 ) which extends on a first ( 20 ), a second ( 21 ) and a third narrow side ( 22 ) of the first wall ( 17 ) to a first height ( 25 ) beyond the cold side ( 19 ), the circumferential edge ( 24 ) extends on a fourth narrow side ( 23 ) to a second shorter height ( 26 ), substantially at the second height ( 26 ), a second wall ( 27 ) lies opposite the cold side ( 19 ) and extends over the width of the fourth narrow side ( 23 ) from the fourth narrow side ( 23 ) and over a part of the length of the narrow sides ( 20, 22 ), which adjoin the fourth narrow side; ( 23 ), the second wall ( 27 ) has an edge ( 29 ) at the end ( 28 ) thereof which faces away from the fourth narrow side ( 23 ), which edge ( 29 ) extends to the first height ( 25 ). Furthermore, a combustion chamber and a gas turbine are disclosed.

The invention relates to a heat-shield element for a combustion chamber, in particular of an annular combustion chamber of a gas turbine installation, and relates to bypassing compressor air around the combustion chamber during partial load. The invention also relates to a combustion chamber and a corresponding gas turbine installation.

As a consequence of lowering the central flame temperature when reducing the power of the gas turbine, the carbon monoxide emissions rise gradually until, from a certain partial load, they exceed the legal emissions limit. This results in a minimum permitted power. However, it may be important to keep the machine ready at very low power.

One possibility for raising the flame temperature and thus reduce the emissions of carbon monoxide consists in guiding part of the compressor outlet air around the combustion and adding it back into the hot gas path upstream of the turbine inlet. Calculations have shown this method to be promising in the case of an annular combustion chamber. What is difficult in this case is that the bypass should be active only in the relevant power ranges, since otherwise the power of the gas turbine is unnecessarily affected. It must therefore be switchable, wherein even when the bypass is switched off no hot gas may enter therein.

With respect to the described prior art, the object of the present invention is, by adding a bypass, to extend the operating range of the gas turbine as much as possible in the direction of low power while conforming to carbon monoxide limits.

A further object of the present invention is to provide an improved combustion chamber.

Finally, it is an object of the present invention to provide an improved gas turbine.

The first object is achieved by a heat-shield element as claimed in claim 1, the second object is achieved by a combustion chamber as claimed in claim 6 and the third object is achieved by a gas turbine as claimed in claim 10.

The dependent claims contain advantageous configurations of the invention.

The invention achieves these objects by providing that, in the case of a heat-shield element, in particular for cladding a combustion chamber wall, comprising a first wall having a hot side which can be exposed to a hot medium, a cold side opposite the hot side and a circumferential edge which extends on a first, a second and a third narrow side substantially up to a first height around the cold side of the first wall, the circumferential edge extends up to a second height, smaller than the first height, on a fourth narrow side, and in that substantially at the second height a second wall lies opposite the cold side and extends over the breadth of the fourth narrow side from the fourth narrow side over part of the length of the narrow sides adjacent to the fourth narrow side, wherein the second wall has, at its end facing away from the fourth narrow side, an edge which extends up to the first height.

The invention is based on the consideration that, in the case of an annular combustion chamber which is mostly clad with ceramic heat-shield elements and only the inlet into the turbine is clad with metallic heat-shield elements, the bypass air should be supplied in the region of the metallic heat-shield elements of the combustion chamber wall since the supply should be effected as far as possible downstream of the combustion in order to prevent cooling of the flame but upstream of the turbine in order to achieve the highest possible gas turbine efficiency. To that end, a new design for the metallic heat-shield elements is required. This design forms the subject matter of this patent application.

The heat-shield element is divided into two regions lying one on top of the other, which are sealed with respect to one another and which form chambers in the installed state, that is to say with the combustion chamber wall. A first chamber extends over the entire surface of the heat-shield element and is used for normal cooling of the metallic heat shield.

A second chamber is located above the first chamber in that part of the heat-shield element oriented toward the turbine.

Advantageously, the heat-shield element consists of a metal or metal alloy which is capable of withstanding high temperatures, as these materials are less brittle than, for example, ceramic and have comparatively good heat- and temperature-conducting behavior.

In one advantageous embodiment, a plurality of cold air openings arranged in the circumferential edge is provided, whence the compressor outlet air provided for cooling the heat-shield element can escape into the combustion chamber.

In that context, it is expedient if the cold air openings are arranged at least in the region of the second wall between the first and the second wall. The cooling openings are thus located in the region of the first chamber for cooling the heat-shield element.

Advantageously, the heat-shield element further comprises an attachment opening whose surround extends from the first wall up to the first height. This ensures that both chambers are sealed with respect to one another and no air can flow from one chamber into the other chamber through the opening necessary for attaching the heat-shield element. The heat-shield element is used to protect a hot gas guiding component from overheating, in particular a combustion chamber, preferably an annular combustion chamber of a gas turbine, having a combustion chamber wall with a burner-side and a turbine-side end, wherein the combustion chamber wall has a circumferential direction. A number of heat-shield elements are preferably arranged circumferentially at the turbine-side end of the combustion chamber wall, respectively forming two chambers, wherein the fourth narrow side is oriented toward the turbine-side end.

The heat-shield elements are preferably attached to the combustion chamber wall by means of attachment bolts.

Preferably, bores are introduced into the combustion chamber wall, such that coolant can be supplied to the heat-shield elements.

In one preferred configuration of the combustion chamber, at least one supply duct per heat-shield element is arranged in the combustion chamber wall in the region of the respective second wall and opens into a plenum which at least partially surrounds the combustion chamber.

The combustion chamber, to which heat-shield elements are attached, is preferably part of a gas turbine. This gas turbine comprises at least one tapping for compressor air, which opens into the plenum via at least one line having a valve.

The invention allows bypass air to be fed into the hot gas path without extensive modifications to hot gas guiding components. The conversion will therefore presumably be comparably cost-effective. It is ensured that, even when the bypass is switched off, no hot gas is drawn in since the second chamber is continuously purged and the outlet therefrom lies, in a flow-favorable manner, between the heat-shield element and the turbine guide vane 1.

The invention will be explained in more detail and by way of example with reference to the drawings, which are diagrammatic and not to scale and in which:

FIG. 1 shows a section through an annular combustion chamber according to the prior art,

FIG. 2 shows a metallic heat-shield element according to the invention and

FIG. 3 shows a section through an annular combustion chamber according to the invention, having a tapping system for the compressor air bypass.

FIG. 1 shows, schematically and by way of example, the combustion system of an annular combustion chamber 1 according to the prior art in a housing 2. The annular combustion chamber 1 consists of a closed ring which is arranged around a rotor axis 3. Burners 4 are arranged in inlet openings 5 in the upper region of the combustion chamber 1. This is where the fuel 6 is mixed with the compressor air 7. The actual combustion takes place in the combustion chamber 1. The hot combustion gases enter the turbine 9 through the outlet at the turbine-side end 8 of the annular combustion chamber 1 and there impinge upon the first static guide vane 10. In order to protect against scaling, the annular combustion chamber 1 is clad with ceramic heat-shield elements 11 and metallic heat-shield elements 12 which are attached to the combustion chamber wall 13.

According to the invention, the bypass air should be supplied in the region of the metallic heat-shield elements 12, since the supply should be effected as far as possible downstream of the combustion in order to avoid cooling the flame, but still upstream of the turbine 9 in order to achieve the highest possible gas turbine efficiency. FIG. 2 shows a metallic heat-shield element 14 according to the invention, which is to be attached to the combustion chamber wall 13 and which forms therewith a first chamber 15 and a second chamber 16 open toward the turbine, which chambers are sealed with respect to one another.

The metallic heat-shield element 14 itself comprises a first wall 17 having a hot side 18 which can be exposed to a hot medium, a cold side 19 opposite the hot side 18 and four narrow sides 20, 21, 22, 23 located therebetween. A circumferential edge 24 extends from each narrow side 20, 21, 22, 23 around the cold side 19. The edge 24 extends on the first 20, the second 21 and the third narrow side 22 substantially up to a first height 25 with respect to the cold side 19 of the first wall 17 and, on the fourth narrow side 23, only up to a smaller second height 26. The installed metallic heat-shield element 14 thus bears against the combustion chamber wall 13 on the edges of three narrow sides 20, 21, 22.

Substantially at the second height 26, a second wall 27 lies opposite the cold side 19. It extends over the breadth of the fourth narrow side 23 and from the fourth narrow side 23 over part of the length of the narrow sides 20, 22 adjacent to the fourth narrow side 23. Furthermore, the second wall 27 has, at its end 28 facing away from the fourth narrow side 23, an edge 29 which extends from the second height 26 up to the first height 25.

For the purpose of cooling the metallic heat-shield element 14, a plurality of cold air openings 30 is provided in the circumferential edge 24 in the region of the first chamber 15.

As with heat-shield elements 12 according to the prior art, the first chamber 15 is supplied, for cooling purposes, with compressor outlet air via bores through the combustion chamber wall 13, which air escapes from the metallic heat-shield element 14 via these cold air openings 30.

The metallic heat-shield element 14 has an attachment opening 31 whose surround 32 extends from the first wall 17 up to the first height 25. The heat-shield element 14 is attached to the combustion chamber wall 13 by means of attachment bolts through this attachment opening 31.

The compressor air supply to the second chamber 16, which is open toward the turbine 9, consists of two components. On one hand, the second chamber 16 is permanently supplied with some compressor air for purging via some bores through the combustion chamber wall 13, such that no hot gas can penetrate into the second chamber 16 if the bypass is switched off.

On the other hand, the second chamber 16 may be switchably exposed to a bypass mass flow rate. This is supplied via comparatively large bores, that is to say in comparison with the bores for purging, in the combustion chamber wall 13. The bypass mass flow rate then escapes via the opening at the trailing edge, that is to say the combustion chamber-side of the heat-shield element 14, at which the circumferential edge 24 reaches only up to a second height 26, into the gap between the metallic heat-shield element 14 and the first static guide vane 10.

FIG. 3 shows how compressor air is first guided out of the gas turbine via a tapping 33 for the bypass. The switching is effected outside the gas turbine by means of a valve 34. The air is then fed back into the gas turbine via a line 35 and is injected into a plenum 36 surrounding the annular combustion chamber 1. Branch lines 37 or branch bores lead from there to the respective second chamber 16 of the respective metallic heat-shield element 14.

In the exemplary embodiment of FIG. 3, only one tapping 33, one valve 34, one line 35 and one plenum 36 are respectively shown. However, solutions having multiple tappings, valves, lines and plena are possible. 

1. A heat-shield element for cladding a combustion chamber wall, the element comprising a first wall having a hot side for being exposed to a hot medium, a cold side opposite the hot side; and a circumferential edge which extends along a top side of a first, a second and a third narrow side at the cold side of the first wall and the circumferential edge is substantially at a first height above and around the cold side of the first wall, the circumferential edge extends to a second height, shorter than the first height, on a fourth narrow side; substantially at the second height a second wall lies opposite and spaced above the cold side and extends over the breadth of the fourth narrow side and from the fourth narrow side the second wall extends over part of the length of the narrow sides that are adjacent to the fourth narrow side; the second wall having an end spaced away from the fourth narrow side and having an edge at the end of the second wall which extends to the first height.
 2. The heat-shield element as claimed in claim 1, comprised of a metal or a metal alloy which is capable of withstanding high temperatures.
 3. The heat-shield element as claimed in claim 1 further comprising a plurality of cold air openings arranged in the circumferential edge.
 4. The heat-shield element as claimed in claim 3, wherein the cold air openings are arranged at least in the region of the second wall and between the first and the second wall.
 5. The heat-shield element as claimed in claim 1, further comprising an attachment opening, and a surround frame around the attachment opening extends from the first wall to the first height.
 6. A combustion chamber comprising a combustion chamber wall with a burner-side and a turbine-side end, wherein the combustion chamber wall has a circumferential direction and is comprised of a number of the heat-shield elements as claimed in claim 1, the heat shield elements are arranged circumferentially in a row at the turbine-side end of the combustion chamber wall and the elements being respectively oriented for forming a first chamber from the first wall to the first height and a second chamber between the first and second walls, and the fourth narrow side is oriented toward the turbine-side end.
 7. The combustion chamber as claimed in claim 6, further comprising attachment bolts for attaching the heat-shield elements to the combustion chamber wall.
 8. The combustion chamber as claimed in claim 6, further comprising bores introduced into the combustion chamber wall for supplying coolant to the heat-shield elements.
 9. The combustion chamber as claimed in claim 6 further comprising at least one supply duct per heat-shield element arranged in the combustion chamber wall in the region of the respective second wall, and a plenum which at least partially surrounds the combustion chamber, and the supply duct opens into the plenum.
 10. A gas turbine having a combustion chamber as claimed in claim 9, wherein the gas turbine comprises at least one tapping located for receiving compressor air, and which opens into the plenum via at least one line having a valve. 